Sometimes you want full-on onion flavor and odor, sometimes you want to tone that intensity down (like when you're adding onions to a salad). Cook's Illustrated, via Cool Tools, says with scientific authority the way you cut an onion can control that intensity.

The way you cut an onion affects its flavor. To prove the point, we took eight onions and cut each two different ways: pole to pole (with the grain) and parallel to the equator (against the grain). We then smelled and tasted pieces from each onion cut each way. The onions sliced pole to pole were clearly less pungent in taste and odor than those cut along the equator.